Helicon wave discharges are known to efficiently produce high-density plasma, and have been exploited as a high density plasma tool for semiconductor processing (etching, deposition, sputtering . . . ) [Lieberman M. A., Lichtenberg A. J., Principles of Plasma Discharges and Materials Processing, J. Wiley & Sons, 1994, New York.], space propulsion and basic plasma experiments. The plasma is usually generated in a cylindrical vacuum vessel in a longitudinal homogeneous magnetic field at 100-300 G or higher. The electromagnetic energy is transferred to the plasma source with frequencies between 1 and 50 MHz, usually with 13.56 MHz for processing plasmas. Helicon waves are generated in the plasma column by specially-shaped antennas.
The most common antenna used to excite helicon waves is the Nagoya Type III antenna [Okamura S, et al. 1986 Nucl. Fusion 26 1491], a modification of which is the double-saddle coil of Boswell [Boswell R. W. 1984, Plasma Phys. Control. Fusion, 26 1147]. Helical antennae were first used by Shoji et al., and have been adapted such that single-loop antennae [Sakawa Y., Koshikawa N, Shoji T, 1996 Appl. Phys. Lett. 69 1695; Carter C. and Khachan J., 1999 Plasma Sources Sci. Technol. 8 432], double loop antennae [Tynan G. R. et al. 1997 J. Vac. Sci. Technol. A 15 2885; Degeling A. W., Jung C. O., Boswell R. W., Ellingboe A. R., 1996 Phys. Plasmas 3 2788], solenoid antennae [Kim J. H., Yun S. M., and Chang H. Y. 1996 Phys. Lett. A 221 94], and bifilar rotating-field antennae [Miljak D. G. and Chen F. F. 1998 Plasma Sources Sci. Technol. 7 61].
The damping of this wave can be explained by collisional theory [Chen F. F., Sudit I. D. and Light M., 1996 Plasma Sources Sci. Technol. 5 173], but collisionless (Landau) damping of helicon waves and the helicon wave transfer through the excitation of another wave at the boundary of the chamber called Trivelpiece-Gould mode has also been discussed [Chen F. F. Physical mechanisms in industrial RF plasma Sources, LTP-104, 2001, UCLA]. The type of discharge achieves electron densities up to 1012-1013 cm−3 in the 0.1 Pa pressure range.
The main features which define the right antenna structure to excite Helicon waves for generation of plasmas are:                Frequency of Excitation: It should be such that the waves satisfies: ωci<ω<ωc (ωci=ion cyclotron frequency, ωc=electron cyclotron frequency). Industrial standard frequency such as 13.56 MHz are usually used in semiconductor processing.        Wave mode: the mode structure of the wave electromagnetic fields generated so that an antenna arrangement can best be designed to efficiently couple the RF power into wave excitation. The two lowest modes are m=0 and m=1 modes. The best way to excite the mode m=0 would be with two loops separated in distance by a half-wavelength. For the mode m=1 there is a natural helical pitch to the electric and magnetic field vectors as the wave propagates along a principal axis. Given the state of the art, the current way to excite this mode is with a helical shaped antenna.        Efficiency of coupling RF power to plasma: the efficiency of the plasma production depends on the coupling of RF energy into the plasma. An important mechanism for damping of the RF energy is Landau damping. The phase velocity of the helicon wave is given by ω/kz where kz, is given by the dispersion relation and depends on the plasma density and magnetic field strength. Ideally, the phase velocity of the wave should be near the maximum of the ionisation potential of the gas we wish to ionise. The higher the value of kz, the higher the density. But if kz is too high then the energy of the electrons may fall below the ionisation potential. It is therefore important to control kz in order to be able to increase the density and control the electron temperature.        
It is known to generate Helicon waves with an apparatus comprises four pairs of electrodes (U.S. Pat. No. 5,146,137, K-H Kretschmer & al., 1992-09-08). A first pair of the electrodes is connected to a first voltage. A second pair of the electrodes is connected to a second voltage. The first voltage is 90.degree. phase shifted relative to the second voltage. The first and second pairs of electrodes are mounted on a first region of the container. The third pair of the electrodes and the fourth pair of the electrodes are then mounted on a second region of the container a distance from the first region of the container. The third and fourth pair of electrodes are connected to phase shifted voltages, in a manner similar to the first and second pair of electrodes. In an alternate aspect, the apparatus generate a plasma inside a container using circularly polarized waves by coupling electromagnetic energy into the plasma through the container wall from the outside: The apparatus comprises four coils. A first coil is connected to a first voltage. A second coil is connected to a second voltage. The first voltage is 90.degree. phase shifted relative to the second voltage. The third and fourth coil are connected to phase shifted voltages, in a manner similar to the first and second coil. In yet a third form, the apparatus comprises four pairs of coils. A first pair of the coils is connected to a first voltage. A second pair of the coils is connected to a second voltage. The first voltage is 90.degree. phase shifted relative to the second voltage. The first and second pairs of coils are mounted on a first region of the container. The third pair of the coils and the fourth pair of the coils are then mounted on a second region of the container a distance from the first region of the container. The third and fourth pair of coils are connected to phase shifted voltages, in a manner similar to the first and second pairs of coils.
The major differences between the previous apparatus and our invention is that our antenna consists in one coil (conductive loop and axial segments are connected) including capacitive elements whereas the apparatus consists in four independent electrodes or coils without connected capacitive elements. Moreover, our invention is a resonant antenna where there is a sinusoidal current distribution in function of the azimutal angle which is not the case for the apparatus.
The conjunction of the plasma source with a process chamber where workpieces are located to either deposit, or etch films or to sputter deposit films to the workpieces is known. This processing system comprises, in particular, external magnet components and RF coils in order to be used as an in situ Nuclear Magnetic Resonance. The use of nuclear magnetic resonance (NMR) for physical, chemical and biological studies is very well developed and highly successful [P. J. Hore, Nuclear Magnetic Resonance, Oxford University Press, Oxford, UK, 1995]. The application of NMR for Plasma diagnostic techniques has recently been undertaken [Zweben S. J. et al., 2003, Rev. Sci. Inst., 74, 1460] for Tokamak experiments. The application of NMR in low pressure and/or temperature plasma processes in particular for moisture monitoring, contamination monitoring, chamber characterizations, in order to reduce the troubleshooting time of the equipment and improve the quality of manufactured devices, is still quite innovative.